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There is ongoing and rapid advancement in approaches to modelling the fate of exhaled particles in different environments relevant to disease transmission. It is important that models are verified by comparison with each other using a common set of input parameters to ensure that model differences can be interpreted in terms of model physics rather than unspecified differences in model input parameters. In this paper, we define parameters necessary for such benchmarking of models of airborne particles exhaled by humans and transported in the environment during breathing and speaking.

Emergency signage conveys exit route information enabling occupants to identify and utilise emergency exits during evacuation. However, it has been frequently demonstrated that static signs are insufficient to attract people's attention. Previous incidents also demonstrate that if exit routes and exits become compromised by the incident, static signs are unable to adapt as required. A goal of the signage industry is to address these limitations while maintaining the clear and unambiguous information conveyed. A signage concept addressing these limitations incorporating a pair of linked adjacent signs, a standard EXIT sign and a text-based ‘NO-EXIT’ sign, is proposed. At any one time, only one sign is activated, displaying either EXIT or NO-EXIT. The active sign can also flash to improve detectability. To assess whether this concept was acceptable, an online international survey, based on the ANSI Z535.3 comprehension test methodology was conducted. The results demonstrate that this novel concept fails to meet the acceptance criteria for safety signs, and as a result, the concept was abandoned by the manufacturer. This study also highlights the importance of conducting comprehension tests for any new safety signage design and the need for composing guidelines for design and application of dynamic signs.

Additional material on breathing rates, exhaled particle size distributions and relative viral loads

Background An issue of concern to the travelling public is the possibility of in-flight transmission of coronavirus disease 2019 (COVID-19) during long- and short-haul flights. The aviation industry maintains that the probability of contracting the illness is small based on reported cases, modelling and data from aerosol dispersion experiments conducted on-board aircraft. Methods Using experimentally derived aerosol dispersion data for a B777-200 aircraft and a modified version of the Wells-Riley equation we estimate inflight infection probability for a range of scenarios involving quanta generation rate and face mask efficiency. Quanta generation rates were selected based on COVID-19 events reported in the literature while mask efficiency was determined from the aerosol dispersion experiments. Results The MID-AFT cabin exhibits the highest infection probability. The calculated maximum individual infection probability (without masks) for a 2-hour flight in this section varies from 4.5% for the ‘Mild Scenario’ to 60.2% for the ‘Severe Scenario’ although the corresponding average infection probability varies from 0.1% to 2.5%. For a 12-hour flight, the corresponding maximum individual infection probability varies from 24.1% to 99.6% and the average infection probability varies from 0.8% to 10.8%. If all passengers wear face masks throughout the 12-hour flight, the average infection probability can be reduced by ~73%/32% for high/low efficiency masks. If face masks are worn by all passengers except during a one-hour meal service, the average infection probability is increased by 59%/8% compared to the situation where the mask is not removed. Conclusions This analysis has demonstrated that while there is a significant reduction in aerosol concentration due to the nature of the cabin ventilation and filtration system, this does not necessarily mean that there is a low probability or risk of in-flight infection. However, mask wearing, particularly high-efficiency ones, significantly reduces this risk.